GPT-5.6 Sol Pro sits at the top of OpenAI's GPT-5.6 family as the highest-capability option, positioned for difficult tasks and longer-running workflows. OpenAI's own description frames the broader GPT-5.6 Sol tier as built for complex work across coding, knowledge work and research, cybersecurity, science, computer use, and design, which signals a general-purpose reasoning model rather than a narrow specialist. Within ChatGPT, Sol Pro powers the dedicated "Pro" reasoning level on eligible paid plans, sitting above the Instant, Medium, High, and Extra High levels that the standard Sol tier covers, which suggests a deliberate ladder where Sol Pro absorbs the longest, deepest chains of thought that the rest of the family offloads downward.
In practical terms, Sol Pro is best understood as a step up in reasoning depth and persistence rather than a different shape of model: it is surfaced through the same ChatGPT model picker and Codex tooling as the rest of the GPT-5.6 line, with Codex access requiring the ChatGPT desktop app's Codex mode at version 26.707.30751 or the Codex CLI at version 0.144.0. OpenAI describes the rollout as gradual across eligible paid plans rather than universal at launch, and introduces a reasoning slider so users can trade latency for depth, a fit that aligns with Sol Pro's positioning as the option for sustained, multi-step work where extra thinking time is worth paying for.
